WO2016048309A1 - Solution de polymère, mat de fibres et ensemble membrane-électrode en nanofibres l'incluant, et son procédé de fabrication - Google Patents

Solution de polymère, mat de fibres et ensemble membrane-électrode en nanofibres l'incluant, et son procédé de fabrication Download PDF

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Publication number
WO2016048309A1
WO2016048309A1 PCT/US2014/057278 US2014057278W WO2016048309A1 WO 2016048309 A1 WO2016048309 A1 WO 2016048309A1 US 2014057278 W US2014057278 W US 2014057278W WO 2016048309 A1 WO2016048309 A1 WO 2016048309A1
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Prior art keywords
particles
fibers
fiber mat
polymer
electrode
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PCT/US2014/057278
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English (en)
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WO2016048309A8 (fr
Inventor
Peter N. Pintauro
Wenjing Zhang
Matthew Brodt
Andrew M. PARK
Jason B. BALLENEE
Ryszard Wycisk
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Vanderbilt University
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Application filed by Vanderbilt University filed Critical Vanderbilt University
Priority to CN201480082069.1A priority Critical patent/CN107408705A/zh
Priority to KR1020177010681A priority patent/KR20170062487A/ko
Priority to PCT/US2014/057278 priority patent/WO2016048309A1/fr
Priority to EP14902314.5A priority patent/EP3198673A4/fr
Priority to JP2017516107A priority patent/JP2017535032A/ja
Priority to CA2962426A priority patent/CA2962426A1/fr
Priority to US15/511,709 priority patent/US20170250431A1/en
Publication of WO2016048309A1 publication Critical patent/WO2016048309A1/fr
Publication of WO2016048309A8 publication Critical patent/WO2016048309A8/fr
Priority to US16/360,151 priority patent/US20190245233A1/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/02—Details
    • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
    • H01M8/023—Porous and characterised by the material
    • H01M8/0239—Organic resins; Organic polymers
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
    • D01D5/00—Formation of filaments, threads, or the like
    • D01D5/0007—Electro-spinning
    • D01D5/0015—Electro-spinning characterised by the initial state of the material
    • D01D5/003—Electro-spinning characterised by the initial state of the material the material being a polymer solution or dispersion
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/8605—Porous electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/8663—Selection of inactive substances as ingredients for catalytic active masses, e.g. binders, fillers
    • H01M4/8668—Binders
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/8663—Selection of inactive substances as ingredients for catalytic active masses, e.g. binders, fillers
    • H01M4/8673—Electrically conductive fillers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/88—Processes of manufacture
    • H01M4/8825—Methods for deposition of the catalytic active composition
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/02—Details
    • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
    • H01M8/023—Porous and characterised by the material
    • H01M8/0241—Composites
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M8/1004—Fuel cells with solid electrolytes characterised by membrane-electrode assemblies [MEA]
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M8/1007—Fuel cells with solid electrolytes with both reactants being gaseous or vaporised
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
    • H01M8/1018—Polymeric electrolyte materials
    • H01M8/1065—Polymeric electrolyte materials characterised by the form, e.g. perforated or wave-shaped
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M2008/1095—Fuel cells with polymeric electrolytes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

Definitions

  • the present invention relates generally to fuel cells, and more particularly, to a fuel cell membrane-electrode-assembly (MEA) having a membrane, an anode electrode and a cathode electrode, where at least one of the electrodes and the membrane is formed of electrospun fibers, a dual or multi fiber mat formed by the electrospun fibers, a polymer solution used to form the electrospun fibers, and methods of forming the same.
  • MEA fuel cell membrane-electrode-assembly
  • Fossil fuels are currently the predominant source of energy in the world. Due to concerns such as carbon dioxide emissions and the finite nature of the supply of fossil fuel, research and development and commercialization of alternative sources of energy have grown significantly over the past decades.
  • One focus of research and development is hydrogen fuel cells, which can quietly and efficiently generate electrical power while producing only heat and water as significant byproducts.
  • PEM proton exchange membrane
  • PEM is a membrane generally made from an ionomer and designed to conduct protons while being impermeable to gases such as oxygen or hydrogen.
  • PEM fuel cells have the potential to replace internal combustion engines, the current dominant source of energy for motor vehicles and other such mobile propulsion applications, and is a promising candidate for emission-free automotive power plants due to its high power output, energy conversion efficiency, and quick start-up.
  • hydrogen molecules are oxidized to hydrogen ions, i.e., protons, and electrons.
  • the protons permeate across a polymer membrane that acts as an electrolyte (the PEM) while the electrons flow through an external circuit and produce electric power.
  • Alkaline anion-exchange membrane fuel cells are a potentially significant technology that could compete with the more popular and well-studied PEM fuel cells for a variety of applications [1].
  • the alkaline anion exchange membrane is a membrane generally made from ionomers with positively charged fixed ion- exchange sites and designed to conduct anions while being impermeable to gases such as oxygen or hydrogen.
  • the present invention relates to an article of manufacture, which includes a fiber mat.
  • the fiber mat includes at least one type of fibers, where the at least one type of fibers includes one or more polymers.
  • the fiber mat is a single fiber mat including one type of fibers, where the one type of fibers includes the one or more polymers.
  • the one type of fibers further includes a plurality of particles of a catalyst.
  • the catalyst includes platinum (Pt) particles, Pt alloy particles, Pt on carbon particles, precious metal particles, precious metal on carbon particles, precious metal based alloys, precious metal based alloys on carbon particles, silver (Ag) particles, nickel (Ni) particles, Ag alloy particles, Ni alloy particles, iron (Fe) particles, Fe alloy particles, palladium (Pd) particles, Pd alloy particles, core-shell catalyst particles, non- platinum group metal (PGM) fuel cell catalysts, or a combination thereof.
  • at least one of the one or more polymers serves as a polymer binder.
  • the polymer binder includes at least one of Nafion and polyvinylidene fluoride (PVDF).
  • the fiber mat is used to form an electrode.
  • the electrode is an anode electrode or a cathode electrode.
  • the fiber mat is a dual or multi fiber mat including a plurality of types of fibers, where each of the plurality of types of fibers includes the one or more polymers.
  • each of the plurality of types of fibers includes a first polymer and a second polymer, and has a different ratio of the first polymer and the second polymer.
  • At least one of the plurality of types of fibers includes a polymer not in another of the plurality of types of fibers.
  • At least one of the plurality of types of fibers further includes a plurality of particles of a catalyst.
  • the catalyst includes platinum (Pt) particles, Pt alloy particles, Pt on carbon particles, precious metal particles, precious metal on carbon particles, precious metal based alloys, precious metal based alloys on carbon particles, silver (Ag) particles, nickel (Ni) particles, Ag alloy particles, Ni alloy particles, iron (Fe) particles, Fe alloy particles, palladium (Pd) particles, Pd alloy particles, core-shell catalyst particles, non-platinum group metal (PGM) fuel cell catalysts, or a combination thereof.
  • At least one of the one or more polymers serves as a polymer binder.
  • the polymer binder includes at least one of Nafion and polyvinylidene fluoride (PVDF).
  • the fiber mat is used to form an electrode.
  • the electrode is an anode electrode or a cathode electrode.
  • the fiber mat is used to form an ion exchange membrane.
  • the ion exchange membrane is a cation exchange membrane or an anion exchange membrane.
  • the fiber mat is usable in an electrochemical device.
  • the electrochemical device is a fuel cell membrane-electrode-assembly (MEA).
  • the fiber mat includes at least one type of fibers, where the at least one type of fibers includes one or more polymers, and a plurality of particles of a catalyst.
  • the electrode is an anode electrode or a cathode electrode.
  • the catalyst includes platinum (Pt) particles, Pt alloy particles, Pt on carbon particles, precious metal particles, precious metal on carbon particles, precious metal based alloys, precious metal based alloys on carbon particles, silver (Ag) particles, nickel (Ni) particles, Ag alloy particles, Ni alloy particles, iron (Fe) particles, Fe alloy particles, palladium (Pd) particles, Pd alloy particles, core-shell catalyst particles, non- platinum group metal (PGM) fuel cell catalysts, or a combination thereof.
  • At least one of the one or more polymers serves as a polymer binder.
  • the polymer binder includes at least one of Nafion and polyvinylidene fluoride (PVDF).
  • the fiber mat is a single fiber mat including one type of fibers, where the one type of fibers includes the one or more polymers and the plurality of particles of the catalyst.
  • the fiber mat is a dual or multi fiber mat including a plurality of types of fibers, where each of the plurality of types of fibers includes the one or more polymers, and at least one of the plurality of types fibers includes the plurality of particles of the catalyst.
  • At least one of the one or more polymers serves as a polymer binder.
  • the polymer binder includes at least one of Nafion and polyvinylidene fluoride (PVDF).
  • each of the plurality of types of fibers includes a first polymer and a second polymer, and has a different ratio of the first polymer and the second polymer.
  • At least one of the plurality of types of fibers includes a polymer not in another of the plurality of types of fibers.
  • a further aspect of the present invention relates to a membrane, which includes a fiber mat.
  • the fiber mat includes at least one type of fibers, where the at least one type of fibers includes one or more polymers.
  • the membrane is an ion exchange membrane.
  • the ion exchange membrane is a cation exchange membrane or an anion exchange membrane.
  • the fiber mat is a single fiber mat including one type of fibers, where the one type of fibers includes the one or more polymers.
  • the fiber mat is a dual or multi fiber mat including a plurality of types of fibers, where each of the plurality of types of fibers includes the one or more polymers.
  • each of the plurality of types of fibers includes a first polymer and a second polymer, and has a different ratio of the first polymer and the second polymer.
  • At least one of the plurality of types of fibers includes a polymer not in another of the plurality of types of fibers.
  • a fuel cell MEA in a further aspect of the present invention, includes: an anode electrode formed by a first fiber mat; a cathode electrode formed by a second fiber mat; and a membrane formed by a third fiber mat, and disposed between the anode electrode and the cathode electrode.
  • each of the first fiber mat, the second fiber mat and the third fiber mat includes at least one type of fibers, where the at least one type of fibers includes one or more polymers; and each of the first fiber mat and the second fiber mat further includes a plurality of particles of a catalyst.
  • the membrane is an ion exchange membrane.
  • the ion exchange membrane is a cation exchange membrane or an anion exchange membrane.
  • At least one of the first fiber mat, the second fiber mat and the third fiber mat is a single fiber mat comprising one type of fibers.
  • At least one of the first fiber mat, the second fiber mat and the third fiber mat is a dual or multi fiber mat comprising a plurality of types of fibers.
  • each of the plurality of types of fibers includes a first polymer and a second polymer, and has a different ratio of the first polymer and the second polymer.
  • At least one of the plurality of types of fibers includes a polymer not in another of the plurality of types of fibers.
  • one of the one or more polymers serves as a polymer binder.
  • the polymer binder includes at least one of Nafion and polyvinylidene fluoride (PVDF).
  • the present invention relates to an electrochemical device having one or more fuel cell MEAs claimed above.
  • FIG. 1 schematically shows a membrane-electrode-assembly (MEA) formed according to one embodiment of the present invention.
  • FIG. 2 shows H2-air fuel cell performance at about 80°C, 100% relative humidity for an entirely electrospun MEA (E-MEA) compared to a standard MEA (Nafion® 212 membrane with decal electrodes).
  • FIG. 3 schematically shows a syringe as a single needle spinneret according to one embodiment of the present invention.
  • FIG. 4A schematically shows a multiple needle spinneret according to one embodiment of the present invention.
  • FIG. 4B schematically shows a multiple needle spinneret in a different perspective view according to one embodiment of the present invention.
  • FIG. 5 schematically shows single orifice spinnerets according to certain
  • FIG. 6 schematically shows a multiple orifice spinneret according to one embodiment of the present invention, where a metal block contains numerous small channels through which the electrospinning solution (or heated polymer/particle melt) is pumped.
  • FIG. 7 schematically shows an electrospinning apparatus for creating a nanofiber mat electrode according to one embodiment of the present invention.
  • FIG. 8 schematically shows a start-stop cycling protocol according to one embodiment of the present invention.
  • FIG. 9 schematically shows a load cycling protocol to assess cathode Pt dissolution in an accelerated durability test according to one embodiment of the present invention.
  • FIG. 10 schematically shows polarization curves for 5 cm 2 MEAs with a Nafion 21 1 membrane and electrospun nanofiber electrodes with cathode and anode Pt loading of 0.10 ⁇ 0.005 mg/cm 2 according to one embodiment of the present invention, where ( ⁇ ) shows TKK TEC10E50E (Pt/HSAC), and ( ⁇ ) shows Johnson Matthey HiSpecTM 4000 (Pt/Vulcan).
  • FIG. 11 schematically shows fuel cell polarization curves for 5 cm 2 MEAs with Tanaka Kikinzoku Kogyo (henceforth abbreviated as TKK) Pt/HSAC catalyst (where HSAC deontes high surface area carbon) and Nafion 21 1 (abbreviated as NR211) membrane operated at 80°C with fully humidified 3 ⁇ 4/air at ambient pressure according to one embodiment of the present invention, where the weight ratios of Pt/HSAC : Nafion : PAA are: ( ⁇ ) 72: 13 : 15, ( ⁇ ) 63 :22: 15, and ( ⁇ ) 55:30: 15 (where PAA is an abbreviation for poly(acrylic acid)).
  • TKK Tanaka Kikinzoku Kogyo
  • HSAC catalyst where HSAC deontes high surface area carbon
  • Nafion 21 1 abbreviated as NR211
  • FIG. 12 schematically shows fuel cell polarization curves for 5 cm 2 MEAs with TKK Pt/HSAC catalyst and NR21 1 membrane operated at 80°C with fully humidified 3 ⁇ 4/air at ambient pressure according to one embodiment of the present invention, where ( ⁇ ) shows electrospun fibers (with PAA), ( ⁇ ) shows painted gas diffusion electrode (abbreviated as GDE) (no PAA), and ( ⁇ ) shows painted GDE (with PAA).
  • GDE painted gas diffusion electrode
  • FIG. 13 shows top-down 6,000x SEM images of an electrospun Pt/C/Nafion/PAA nanofiber mat with an average fiber diamter of (a) 250 nm and (b) 475 nm according to certain embodiments of the present invention.
  • FIG. 14A schematically shows the effect of electrode structure on MEA performance with Johnson Matthey (JM) Pt/Vulcan catalyst using nanofiber electrode MEA and traditonal spray-coated MEA at 100% RH according to certain embodiments of the present invention.
  • JM Johnson Matthey
  • FIG. 14B schematically shows the effect of electrode structure on MEA performance with JM Pt/Vulcan catalyst using nanofiber electrode MEA and traditonal spray-coated electrode MEA at 40% relative humidity (RH) according to certain embodiments of the present invention.
  • FIG. 15A schematically shows the effect of electrode structure on MEA durability showing nanofiber electrospun and traditonal spray-coated MEAs using JM Pt/Vulcan catalyst at 100% RH according to certain embodiments of the present invention.
  • FIG. 15B schematically shows the effect of electrode structure on MEA durability showing nanofiber electrospun and traditonal spray-coated MEAs using JM Pt/Vulcan catalyst at 40% RH according to certain embodiments of the present invention.
  • FIG. 16 schematically shows real time measurement of ppm CO 2 at the cathode exhaust during start-stop potential cycling (100% RH condition) of nanofiber electrode and traditional spray-coated MEAs using JM Pt/Vulcan catalyst according to certain
  • FIG. 17 schematically shows carbon loss calculated from data as shown in FIG. 16 according to certain embodiments of the present invention.
  • FIG. 18 schematically shows top-down 6,000x SEM image of an electrospun fiber mat with Pt/C catalyst particles with a binder of (a) Nafion+PVDF and (b) PVDF according to certain embodiments of the present invention.
  • FIG. 19 schematically shows power density curves for 5 cm 2 MEAs with a Nafion 211 membrane and cathode and anode Pt loading of 0.10 mg/cm 2 with Johnson Matthey HiSpec 4000 catalyst according to certain embodiments of the present invention.
  • FIG. 20 schematically shows power density and polarization curves for a 5 cm 2 MEA with a Nafion 21 1 membrane and a nanofiber cathode and anode according to certain embodiments of the present invention.
  • first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the invention.
  • relative terms such as “lower” or “bottom” and “upper” or “top”, may be used herein to describe one element's relationship to another element as illustrated in the Figures. It will be understood that relative terms are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures. For example, if the device in one of the figures is turned over, elements described as being on the “lower” side of other elements would then be oriented on “upper” sides of the other elements. The exemplary term “lower” can, therefore, encompass both an orientation of "lower” and
  • PEM proton exchange membrane
  • anion exchange membrane or its abbreviation "AEM”, as used herein, refer to a membrane generally made from ionomers and designed to conduct anions.
  • anion exchange membrane fuel cell or “AEM fuel cell”, or its abbreviation
  • AEMFC refers to a fuel cell using the AEM.
  • conducting polymer or "ionomer” generally refers to a polymer that conducts ions. More precisely, the ionomer refers to a polymer that includes repeat units of at least a fraction of ionized units.
  • polyelectrolyte generally refers to a type of ionomer, and particularly a polymer whose repeating units bear an electrolyte group, which will dissociate when the polymer is exposed to aqueous solutions (such as water), making the polymer charged.
  • the conducting polymers, ionomers and polyelectrolytes may be generally referred to as "charged polymers".
  • polyelectrolyte fiber or “charged polymer fiber” generally refer to the polymer fiber formed by polyelectrolytes or the likes. As used herein, polyelectrolyte, ionomer, and charged polymer can be used interchangeably.
  • the terms “uncharged polymer” or “uncharged (or minimally charged) polymer” generally refer to the polymer that does not effectively conduct ions, particularly to the polymer whose repeating units do not bear an electrolyte group or bear a small number of electrolyte groups, and thus the polymer will not be charged or will have a very small charge when being exposed to aqueous solutions.
  • the terms “uncharged polymer fiber” or “uncharged (or minimally charged) polymer fiber” generally refer to the polymer fiber formed by the uncharged/uncharged (or minimally charged) polymer.
  • nanostructure generally refers to elements or articles having widths or diameters of less than about 1 ⁇ .
  • specified widths can be smallest width (i.e. a width as specified where, at that location, the article can have a larger width in a different dimension), or largest width (i.e. where, at that location, the article's width is no wider than as specified, but can have a length that is greater).
  • the sizes of the nanostructures refer to the number of dimensions on the nanoscale.
  • nanotextured surfaces have one dimension on the nanoscale, i.e., only the thickness of the surface of an object is between 1.0 and 1000.0 nm.
  • Nanowires have two dimensions on the nanoscale, i.e., the diameter of the tube is between 1.0 and 1000.0 nm; its length could be much greater.
  • sphere-like nanoparticles have three dimensions on the nanoscale, i.e., the particle is between 1.0 and 1000.0 nm in each spatial dimension.
  • a list of nanostructures includes, but not limited to, nanoparticle, nanocomposite, quantum dot, nanofilm, nanoshell, nanofiber, nanowire, nanotree, nanobrush, nanotube, nanorod, and so on.
  • this invention relates to an integration/combination of nano fiber electrodes with a nanofiber-based membrane or nanofiber electrodes with a non-nanofiber based membrane to create a fuel cell membrane-electrode-assembly (MEA) for an electrochemical device, where each of the nanofiber electrodes and the nanofiber membrane is fabricated by an
  • the electrospinning process typically involves applying a high voltage electric field to a spinneret needle containing a polymer solution or polymer melt. Charges on the surface of the solution as it emerges from the spinneret overcome the surface tension such as to produce and eject a thin liquid jet of the solution from the tip of the spinneret needle. As the jet of electrified solution travels towards a collector with a different electric potential, electrostatic repulsion from surface charges causes the diameter of the jet to narrow. The jet may enter a whipping mode and thereby be stretched and further narrowed due to instabilities in the electric field. Solid fibers are produced as the jet dries and the fibers accumulate on the collector to form a non- woven material.
  • the fiber mat includes at least one type of fibers, where the at least one type of fibers includes one or more polymers.
  • the fiber mat is a single fiber mat including one type of fibers, where the one type of fibers includes the one or more polymers.
  • the one type of fibers further includes a plurality of particles of a catalyst.
  • the catalyst includes platinum (Pt) particles, Pt alloy particles, Pt on carbon particles, precious metal particles, precious metal on carbon particles, precious metal based alloys, precious metal based alloys on carbon particles, silver (Ag) particles, nickel (Ni) particles, Ag alloy particles, Ni alloy particles, iron (Fe) particles, Fe alloy particles, palladium (Pd) particles, Pd alloy particles, core-shell catalyst particles, non- platinum group metal (PGM) fuel cell catalysts, or a combination thereof.
  • at least one of the one or more polymers serves as a polymer binder.
  • the polymer binder includes at least one of Nafion and polyvinylidene fluoride (PVDF).
  • the polymer binder may include Nafion only, PVDF only, or both Nafion and PVDF.
  • the fiber mat is a dual or multi fiber mat including a plurality of types of fibers, where each of the plurality of types of fibers includes the one or more polymers. In other words, two or more types of fibers are in the dual or multi fiber mat.
  • At least one of the plurality of types of fibers is configured to melt to fill in a space between the other of the plurality of types of fibers.
  • one of the types of fibers may be melted to fill in the space between other fibers.
  • each of the plurality of types of fibers may include the same type of polymers having different ratios.
  • each of the plurality of types of fibers may include a first polymer and a second polymer, and has a different ratio of the first polymer and the second polymer.
  • each of the plurality of types of fibers may include at least one different type of polymers.
  • at least one of the plurality of types of fibers may include a polymer not in another of the plurality of types of fibers.
  • At least one of the plurality of types of fibers further includes a plurality of particles of a catalyst.
  • the catalyst includes platinum (Pt) particles, Pt alloy particles, Pt on carbon particles, precious metal particles, precious metal on carbon particles, precious metal based alloys, precious metal based alloys on carbon particles, silver (Ag) particles, nickel (Ni) particles, Ag alloy particles, Ni alloy particles, iron (Fe) particles, Fe alloy particles, palladium (Pd) particles, Pd alloy particles, core-shell catalyst particles, non-platinum group metal (PGM) fuel cell catalysts, or a combination thereof.
  • At least one of the one or more polymers serves as a polymer binder.
  • the polymer binder includes at least one of Nafion and polyvinylidene fluoride (PVDF).
  • the fiber mat having the particles may be used to form an electrode.
  • the electrode is an anode electrode or a cathode electrode.
  • the fiber mat without the particles may be used to form an ion exchange membrane.
  • the ion exchange membrane is a cation exchange membrane or an anion exchange membrane.
  • the fiber mat is usable in an electrochemical device.
  • the electrochemical device is a fuel cell membrane-electrode-assembly (MEA).
  • the fuel cell MEA may include an anode electrode formed by a first fiber mat; a cathode electrode formed by a second fiber mat; and a membrane formed by a third fiber mat, and disposed between the anode electrode and the cathode electrode.
  • Each of the first, second and third fiber mats may be the same or different fiber mats as described above.
  • an MEA 100 is shown according to one embodiment of the present invention.
  • the MEA 100 in use may be incorporated into an electrochemical device, for example, a proton exchange membrane (PEM) fuel cell.
  • the MEA 100 has an anode electrode 110, a cathode electrode 120, and a membrane 130, where the anode electrode 1 10 and the cathode electrode 120 are respectively attached to the opposing surfaces of the membrane 130.
  • one or both electrodes 110 and/or 120 are formed of electrospun nanofibers, and the membrane 130 contains electrospun nanofibers.
  • Embodiments of the nano fiber membrane and the nano fiber electrodes and their fabrications are respectively disclosed in co-pending U.S. patent application Nos. 13/567,857 and 13/823,968, which are incorporated herein in their entireties by reference. Please refer to the disclosures of co-pending U.S. patent application Nos. 13/567,857 and 13/823,968 for the details.
  • the thickness of each of the anode electrode 110 and the cathode electrode 120 may be about 1-30 microns, and the thickness of the membrane 130 may be about 10-200 microns. The following description summarizes only the key features of the nano fiber membrane and the nanofiber electrodes and their fabrications.
  • the membrane 130 is ionically conductive, or proton conductive. In one
  • the membrane includes nanofibers of an uncharged (or minimally charged) polymer surrounded by a matrix of a proton conducting polymer. In another embodiment, the membrane includes nanofibers of a proton conducting polymer surrounded by a matrix of an uncharged (or minimally charged) polymer.
  • the uncharged (or minimally charged) polymer is polyphenylsulfone
  • the proton conducting polymer is a perfluorosulfonic acid polymer. In one embodiment, the perfluorosulfonic acid polymer is Nafion ® .
  • the fiber mat may be a single fiber mat, a dual fiber mat, or a multi fiber mat.
  • the single fiber mat is formed of a single polymer fiber, which is generated by performing fiber electrospinning on one polymer solution.
  • the dual or multi fiber mat is formed of one or more first-type polymer fibers and one or more second-type polymer fibers.
  • the dual or multi fiber mat is formed by dual or multi fiber electrospinning, using two or more different polymer solutions to generate the two or more different types of polymer fibers.
  • the polymer fiber used to form the membrane 130 may be different from either one of the polymer fibers used to form the anode electrode 1 10 and the cathode electrode 120.
  • the anode electrode 110 and the cathode electrode 120 may be formed of a single fiber mat of one type of polymer fiber.
  • the polymer solution used to form the polymer fiber is formed by a solvent and a polymer solute distributed in the solvent.
  • the polymer solute includes a plurality of particles of a catalyst, and a polymer binder distributed thereon.
  • the polymer fiber includes the particles of the catalyst and the polymer binder, and may include a part of the solvent.
  • the polymer binder used to form the anode electrode 1 10 and the cathode electrode 120 may include DuPont's Nafion® and polyvinylidene fluoride, which is henceforth abbreviated as PVDF.
  • the membrane 130 includes a fiber network, formed from a dual or multi fiber mat of one or more first-type polymer fibers and one or more second-type polymer fibers; and a polymer matrix encompassing the fiber network, where the polymer matrix is formed by softening and flowing at least one of the one or more of the first-type polymer fibers of the dual or multi fiber mat to fill in the void space between the one or more second-type polymer fibers of the dual or multi fiber mat, or by softening and flowing at least one of the one or more of the second-type polymer fibers of the dual or multi fiber mat to fill in the void space between the one or more first-type polymer fibers of the dual or multi fiber mat.
  • the one or more first-type polymer fibers include charged polymer fibers or charged polymer precursor fibers, and the one or more second-type polymer fibers include uncharged polymer fibers.
  • the polymer solution used to form the polymer fiber is formed by a solvent and a polymer solute distributed in the solvent.
  • the polymer solute includes a polymer, but does not include any particles.
  • the polymer fiber formed includes the polymer, and may include a part of the solvent.
  • the polymer solute includes a polymer and particles of the catalyst.
  • the one or more first-type polymer fibers include proton conducting polymer fibers
  • the one or more second-type polymer fibers includes uncharged (or minimally charged) polymer fibers.
  • the uncharged (or minimally charged) polymer is polyphenylsulfone
  • the proton conducting polymer is a perfluorosulfonic acid polymer.
  • the membrane is fabricated by the following steps: At first, one or more first-type polymer solutions are formed from one or more first-type polymers and one or more second-type polymer solutions from one or more second-type polymers, respectively. Each of the one or more first-type polymers includes a charged polymer, while each of the one or more second-type polymers includes a uncharged (or minimally charged) polymer. Next, the one or more first-type polymer solutions and the one or more second-type polymer solutions are electrospun, separately and simultaneously, to form a dual or multi fiber mat of one or more first-type polymer fibers and one or more second-type polymer fibers.
  • the dual or multi fiber mat is processed by softening and flowing at least one of the one or more first-type polymer fibers to fill in the void space between the one or more second-types polymer fibers, or by softening and flowing at least one of the one or more second-type polymer fibers to fill in the void space between the one or more first-types polymer fibers, so as to form the membrane.
  • the processing step includes the steps of compressing the dual or multi fiber mat; and thermal annealing the dual or multi fiber mat to soften and flow at least one of the one or more first-type polymer fibers to fill in the void space between the one or more second-type polymer fibers.
  • the processing step includes the steps of compressing the dual or multi fiber mat; and exposing the dual or multi fiber mat to solvent vapor to soften and flow at least one of the one or more second-type polymer fibers to fill in the void space between the one or more first-type polymer fibers. In one embodiment, the processing step further includes the steps of thermal annealing the dual or multi fiber mat.
  • each of the anode and cathode electrodes includes a catalyst.
  • the catalyst includes platinum-supported carbon (Pt/C).
  • At least one of the anode electrode and the cathode electrode is formed of nano fibers by electrospinning of a polymer solution containing the catalyst and an ionomer or an uncharged (or minimally charged) polymer.
  • the ionomer polymer includes Nafion ® .
  • the uncharged polymer includes PVDF.
  • each of the anode electrode and the cathode electrode is fabricated by forming a polymer solution containing the catalyst and the ionomer or an uncharged (or minimally charged) polymer; electrospinning the polymer solution to generate electrospun fibers so as to form a nanofiber mat; and pressing the nanofiber mat to fabricate the electrode.
  • the anode and cathode electrodes are separated by a PEM.
  • the MEA is disposed between two flow-field plates, and in operation, hydrogen and air or some other fuel and oxidant are provided to the electrodes of the MEA via channels that are formed in the flow field plates. More particularly, one flow-field plate directs hydrogen to the anode and another flow-field plate directs oxygen in the air to the cathode.
  • a catalyst layer facilitates separation of the hydrogen into protons and electrons. Free electrons produced at the anode are conducted as a usable electric current through an external circuit.
  • hydrogen protons that have passed through the PEM come together with oxygen in air and electrons that return from the external circuit, to form water and heat.
  • the fuel cell MEA may also have a first gas diffusion layer disposed between the anode electrode and the anode gas channel; and a second gas diffusion layer disposed between the cathode electrode and the cathode gas channel.
  • the first and second gas diffusion layers are formed of electrospun nanofibers.
  • a first entirely electrospun fuel cell MEA has been fabricated (e.g., a fuel cell MEA containing an electrospun anode, an electrospun cathode and an electrospun membrane).
  • the electrospun membrane has been shown to provide enhanced fuel cell durability relative to commercial Nafion® films, while the electrospun electrodes have been shown to provide enhanced fuel cell power output and durability, as compared to conventional/benchmark "decal" electrodes [4, 5].
  • decal electrodes on a commercial Nafion® membrane or catalyst coated gas diffusion layers that are hot pressed onto a proton conducting membrane i.e., decal electrodes on a commercial Nafion® membrane or catalyst coated gas diffusion layers that are hot pressed onto a proton conducting membrane.
  • the electrospun MEA was constructed by separately preparing an electrospun membrane and electrospun electrodes (anode and cathode) and then hot-pressing the components into a single MEA construct.
  • the fuel cell MEA can also be fabricated by forming a first electrospun nanofiber electrode; sequentially forming a electrospun nanofiber membrane on the first electrospun nanofiber electrode; and sequentially forming a second electrospun nanofiber electrode on the electrospun nanofiber membrane to construct the fuel cell MEA, where one of the first and second electrospun nanofiber electrodes is an anode electrode, and the other of the first and second electrospun nanofiber electrodes is a cathode electrode.
  • the membrane is formed such that a proton conducting polymer is reinforced by an electrospun nanofiber mat of an uncharged polymer.
  • a membrane is formed such that the uncharged polymer surrounds an electrospun mat of proton conducting nanofibers, or one electrode (e.g., the anode) contains no nanofiber in structure, can also be utilized to the practice the invention.
  • Nafion® and polyethylene oxide (PEO) solutions were prepared by dissolving Nafion® powder (prepared by evaporating the solvent from LIQUION 11 15, Ion Power, Inc.) and PEO powder (Sigma-Aldrich, 400 kDa MW) into a 2: 1 weight ratio n- propanohwater mixture. These two solutions were then combined to form a Nafion®/PEO electrospinning solution where the PEO constituted about 1 wt% of the total polymer content.
  • a polyphenylsulfone (Radel ® R 5500NT, 63 kDa MW, from Solvay Advanced Polymers, LLC) solution was prepared by dissolving polymer powder in an 80:20 wt. ratio of n-methyl-2-pyrrolidone:acetone.
  • Nafion®/PEO solution were each drawn into separate syringes and electrospun using a 22 gauge needle (Hamilton Company). PPSU fibers and Nafion®/PEO fibers were
  • the flow rates and concentrations of the Nafion®/PEO and the PPSU were varied to produce fiber mats of varying compositions (i.e., different Nafion® volume fractions).
  • the Nafion®/PEO solution was electrospun at a flow rate of about 0.20 mL/hr and a concentration of about 20 wt%.
  • the PPSU solution was electrospun at a flow rate of about 0.038 mL/hr, at a constant concentration of about 25 wt%.
  • a spinneret-to- collector distance (SCD) was fixed at about 6.5 cm and the voltage was set at about 4.15 kV.
  • the PPSU solution was electrospun at about 8.5 kV with an SCD of about 8.5 cm. All electrospinning experiments were performed at room temperature, where the relative humidity was about 35%.
  • the electrospun dual nanofiber mat was compressed at about 15,000 psi and about 127°C for about 10 seconds.
  • the sample was rotated 90° three times and successively compressed to ensure even compression.
  • the dual nanofiber mat was then annealed in vacuum at about 150°C for about 2 hours so as to produce the membrane.
  • the resulting membrane, where PPSU nanofibers are embedded in a Nafion® polymer matrix, was boiled in about 1 M sulfuric acid and deionized water for about one hour each to remove residual PEO and to protonate all ion-exchange sites.
  • An electrospinning cathode dispersion (ink) was prepared by mixing Pt/C particles
  • the ink was pumped out of a needle spinneret (a 22 gauge needle) and deformed into a Taylor cone by the strong applied potential at the needle tip, +7.0 kV relative to a grounded stainless steel rotating drum nanofiber collector.
  • the spinneret-to-collector distance was fixed at about 9 cm, and the flow rate of ink was about 1.5 mL-lf 1 .
  • Nanofibers were collected on an aluminum foil that was fixed to the collector drum (rotating at about 100 rpm). The drum oscillated horizontally to improve the uniformity of deposited nanofibers.
  • the electrospun nanofiber mat Prior to hot-pressing, the electrospun nanofiber mat was pre-compressed between two PTFE sheets under mild pressure (about 217 Pa). The Pt-loading of the nanofiber mat was calculated from its total weight and the weight- fraction of Pt/C catalyst used for its preparation.
  • the anode and cathode electrodes and the membrane were prepared separately.
  • E-MEAs could also be fabricated by successively (sequentially) electrospinning nanofibers for the anode, the membrane, and the cathode and then processing the entire E-MEA simultaneously.
  • the membrane and electrodes were prepared separately, and the electrospun electrodes were hot-pressed onto the electrospun membrane at about 283°F and about 100 psi for about 10 minutes.
  • the E-MEA was then loaded into a fuel cell test fixture and pre-conditioned for about 3 hours at about 80°C by successively running the fuel cell for about 2 minutes at low current density (about 150 mA/cm 2 ) and about 2 minutes at low voltage (about 0.2V). Fuel cell performance at about 80°C and about 100% relative humidity was then measured with a Scribner Fuel Cell Test Station. For comparison, similar MEA preparation/conditioning steps were performed using a commercial Nafion® membrane and decal electrodes. The Nafion®/decal MEA had the same loading of Pt catalyst in the electrodes (about 0.15 mg/cm 2 each for the anode and cathode) and the electrospun MEA.
  • the fuel cell performance for both MEAs is shown in FIG. 2. As shown in FIG. 2, ( ⁇ ) indicates E-MEA voltage vs. current density, ( ⁇ ) indicates E-MEA power density vs. current density, ( ⁇ ) indicates Nafion/decal voltage vs. current density, and (o
  • the E-MEA was composed of an about 30 ⁇ thick Nafion®/polyphenylsulfone electrospun membrane in which Nafion was reinforced by polyphenylsulfone nanofibers and the Nafion® content was about 65 vol%.
  • the E-MEA anode and cathode were electrospun nanofiber mats having about 72 wt% Pt/C, about 13 wt% Nafion®, about 15 wt% PAA. Each electrode had a Pt loading of about 0.15 mg/cm 2 .
  • the Nafion®/decal MEA was a Nafion® 212 membrane (51 ⁇ thick) with decal electrodes (about 0.15 mg/cm 2 Pt loading and was about 77 wt% Pt/C and about 23 wt% Nafion® binder).
  • the E-MEA produced more power than the standard Nafion®/decal MEA at all operating voltages (the measured current density was higher at all cell voltages).
  • the E-MEA has a power output of about 480 mW/cm 2 , as compared to about 377 mW/cm 2 for a Nafion®/decal MEA, which is a 27% improvement.
  • the maximum power for the E-MEA is about 516 mW/cm 2 , as compared to about 460 mW/cm 2 for the Nafion®/decal MEA.
  • the present invention recites an entirely electrospun fuel cell MEA containing an electrospun anode, an electrospun cathode and an electrospun membrane, for the first time, which has considerable advantages over a conventional Nafion®/decal MEA.
  • Nanofiber electrode mats can be created using equipment with different types of spinneret equipments. Some spinnerets can be termed “needle” spinnerets, whereas other equipment employs orifice (needleless) spinnerets or electrospinning equipment that does not rely on the use of a spinneret.
  • the generated particle/binder electrodes or nanofiber membrane may be generated using: (1) a single needle spinneret, or (2) a multiple needle spinneret.
  • the single needle spinneret in its simplest manifestation, is just a hypodermic needle syringe filled with the electrospinning solutions, which was used in the examples listed in the present disclosure.
  • the configuration of the single needle spinneret may be a syringe.
  • FIG. 3 schematically shows a syringe as a single needle spinneret according to one embodiment of the present invention. Specifically, FIG. 3 shows a cartoon sketch of such a syringe 300.
  • FIGS. 4A and 4B show multiple needle spinnerets, in different perspective views, according to certain embodiments of the present invention. As shown in FIG. 4A, the multiple needle spinneret 400 has a plurality of needles.
  • the generated particle/binder electrodes or nanofiber membrane may be generated using: (3) a single orifice spinneret, or (4) a multiple orifice spinneret.
  • the single orifice spinneret or the multiple orifice spinneret may include the structure where a polymer solution or melt is forced through a small channel or multiple channels in a metal block, which is polarized at a high potential to create an electrospun fiber.
  • FIG. 5 schematically shows single orifice spinnerets according to certain embodiments of the present invention. As shown in FIG.
  • FIG. 5 shows a photo of a single orifice spinneret.
  • FIG. 6 schematically shows a multiple orifice spinneret according to one embodiment of the present invention. As shown in FIG. 6, the multiple orifice spinneret 600 may include a structure where a metal block contains numerous small channels 610 through which the electrospinning solution (or heated polymer/particle melt) is pumped, as shown schematically in FIG. 6.
  • nanofiber electrodes using electrospinning equipment that does not utilize a needle or orifice spinneret.
  • the electrospinning may be performed using the commercially available needle- free electrospinning NanospiderTM Technology patented by Elmarco Inc.
  • a polarized electrode is partially submerged or coated in a polymer solution, where one or many fiber filaments emerging from the free liquid surface [6].
  • the nanofibers may be created without the application of an electric field.
  • ForcespinningTM [7] has been developed to make nanofibers from a wide range of materials. This new method uses centrifugal force, rather than and electric field, as occurs in a typical electrospinning process.
  • each solution contains a solvent, catalyst electrode particles, and a suitable binder.
  • the binder is a proton conducting ionomer, such as a perfluorosulfonic acid polymer (e.g., DuPont's Nafion® or Solvay's Aquivion®) or a sulfonated hydrocarbon polymer.
  • a perfluorosulfonic acid polymer e.g., DuPont's Nafion® or Solvay's Aquivion®
  • a carrier polymer such as poly(acrylic acid), abbreviated as PAA.
  • the binder is an uncharged polymer, such as PVDF. Nafion may also be mixed with PVDF and this mixture used as a catalyst binder for nanofiber electrodes.
  • PVDF uncharged polymer
  • Nafion may also be mixed with PVDF and this mixture used as a catalyst binder for nanofiber electrodes.
  • One skilled in the art should also recognize that, in principle, one could electrospin catalyst binder nanofibers from a high temperature polymer melt without the use of a solvent by heating suitably chosen polymer/catalyst mixtures.
  • the catalyst particles (powder) and polymer binder are mixed with a suitable solvent such an alcohol/water mixture or an acetone/water mixture, where the alcohol is, for example, methanol, ethanol, isopropanol, n-propanol or a mixture of alcohols.
  • a suitable solvent such as an alcohol/water mixture or an acetone/water mixture, where the alcohol is, for example, methanol, ethanol, isopropanol, n-propanol or a mixture of alcohols.
  • the total polymer and catalyst powder content of the electrospinning suspensions is typically between about 10-18 wt%, with the remaining wt% portion being solvent.
  • the catalyst can be any electrically conducting electrode powder material, including Pt on carbon powder, a metal black powder such at Pt-black or Pd-black, a carbon-based non precious metal fuel cell catalyst, metal alloy and core-shell catalyst powders, or a precious metal on a non-carbon support.
  • Table 1 lists examples of the range of composition of electrospun fiber electrodes, after solvent evaporation, in terms of the wt% of catalyst and polymer binder. Compositions are listed in terms of weight percentages of the final dry nano fiber mats.
  • the Pt/C catalyst was Pt on carbon from either Johnson Matthey Company or Tanaka Kikinzoku Kogyo.
  • a series of electrospun nanofiber mat electrodes with two different commercial Pt/C catalysts and 1 100 EW Nafion ® and poly(acrylic acid) binder were fabricated and evaluated.
  • the electrodes were formed into membrane-electrode-assemblies (MEAs) using Nafion 21 1 as the membrane.
  • MEAs membrane-electrode-assemblies
  • the effects of catalyst type, nanofiber composition (the ratio of Pt/C to Nafion), and fiber diameter on hydrogen/air fuel cell power output were investigated using 5 cm 2 MEAs. In general, these variations in the anode and cathode had little or no impact on fuel cell performance.
  • Cathode durability studies were performed, where nanofiber and conventional sprayed gas diffusion electrode MEAs were compared. MEA durability was evaluated under an automotive-specific start-stop cycling (carbon corrosion) protocol. The beginning of life (BoL) and end of life (EoL) performance of the nanofiber electrodes after durability cycling were compared with conventional
  • a commercial Pt/C catalyst powder either Johnson Matthey (JM) HiSpecTM 4000 (40% Pt on Vulcan carbon), henceforth referred to as JM Pt(Vulcan), or Tanaka Kikinzoku Kogyo TEC10E50E (46.1% Pt on high surface area Ketjen
  • Nafion forms micelles in alcohol/water mixture and will not electrospin into well-formed fibers, unless a suitable carrier polymer is added to the electrospinning solution [8].
  • a suitable carrier polymer is added to the electrospinning solution [8].
  • PAA poly acrylic acid
  • a suspension of Nafion and catalyst was first sonicated for 90 minutes with intermittent mechanical stirring before the addition of poly(acrylic acid). The entire mixture was then mechanically stirred for approximately 48 hours.
  • the total polymer and powder content of the spinning suspensions was between 10-18 wt.%, and the Pt/C:Nafion:PAA weight ratio was varied so that the dry mat contained 55-72 wt.% Pt/C and 13-30 wt.%> Nafion, where the PAA content was held constant at 15 wt.%.
  • the inks were drawn into a 3 mL syringe and electrospun using a 22- gauge stainless steel needle spinneret, where the needle tip was polarized to a potential of 8- 12 kV relative to a grounded stainless steel rotating drum collector that was operated at a rotation speed of 100 rpm.
  • FIG. 7 schematically shows an electrospinning apparatus for creating a nanofiber mat electrode according to one embodiment of the present invention.
  • electrospinning was performed at room temperature in a custom-built environmental chamber, where the relative humidity was maintained constant at 40%.
  • MEAs with nanofiber electrodes were fabricated at Vanderbilt University by hot pressing 5 or 25 cm 2 electrospun electrodes (anodes and cathodes of identical fiber composition) onto opposing sides of a Nafion 211 membrane (NR211) at 140 C and 4 MPa for 1 minute, after a 10-minute heating period at 140 C and 0 MPa.
  • the Pt loading of a nanofiber mat was calculated from its total electrode weight and the weight- fraction of Pt/C catalyst used in the electrospinning ink.
  • a carbon paper gas diffusion layer (GDL) (Sigracet 25 BCH GDL) was physically pressed onto the MEA's anode and cathode in the test fixture.
  • Painted gas diffusion electrodes were also fabricated at Vanderbilt University with and without PAA. Pt/C powder was mixed with a commercial Nafion dispersion in alcohol/water. PAA was added to some inks. The inks were painted in multiple layers directly onto the carbon gas diffusion paper (Sigracet GDL 25 BCH) and dried at 70°C for 30 min after each painted layer. Painted GDEs with PAA were prepared with a composition of 72 wt.% TKK Pt/HSAC, 13 wt.% Nafion, and 15 wt.% PAA (the same as some electrospun fibers tested).
  • GDEs without PAA were prepared with a composition of 67 wt.% Pt/HSAC and 33 wt.% Nafion. These 5 cm 2 GDEs were hot pressed onto NR21 1 membranes with fuel cell test fixture gaskets at the same conditions as those employed for the electrospun electrodes.
  • GDEs Traditional sprayed gas diffusion electrodes
  • NTCNA Nissan Technical Center North America
  • MEAs were prepared by hot pressing traditional Pt/C gas diffusion electrode (GDE) anodes, catalyst-coated experimental GDE cathodes, and NR21 1 membranes.
  • fuel cell polarization curves were performed on 5 cm 2 MEAs. These data were collected using a Scribner Series 850e test station with mass flow, temperature, and manual backpressure control.
  • the fuel cell test fixture accommodated a single MEA and contained single anode and cathode serpentine flow channels. Experiments in 3 ⁇ 4/air were performed at 80°C with fully humidified gases at atmospheric (ambient) pressure, with a 3 ⁇ 4 flow rate of 125 seem and an airflow rate of 500 seem.
  • the MEAs Prior to collecting polarization data, the MEAs were pre-conditioned by operating at 80°C and 1 A/cm 2 for 8 hours after shorter periods of lower current densities. Polarization curves were generated by measuring the current at a given voltage after waiting 60 seconds for system stabilization. The polarization curves were measured in the anodic (positive) direction.
  • Constant gas flow rates used for these evaluations were high, 8.0 normal liters per minute (NLPM) at the cathode and 4.0 NLPM at the anode, with no/minimal pressure drop across the flow field.
  • cathode catalyst mass activity data were collected with a current-controlled anodic scan (high current to low current) at 80°C with fully humidified (3 ⁇ 4 and H 2 gas feeds at 1.0 bar g , where the system was allowed to stabilize for three minutes at each data point. Mass activities were determined from a plot of IR- free voltage verse the I3 ⁇ 4-crossover corrected current density.
  • ECA Electrochemical Surface Area
  • In-situ cyclic voltammetry (CV) measurements were performed at NTCNA on 25 cm 2 MEAs with a sweep rate 20 mV/s, where a H 2 -purged anode served as both the counter and reference electrodes and 2 was fed to the working cathode.
  • the fuel cell test fixture was operated at 30°C with gas feed streams at a dew point of 30°C (fully humidified).
  • the CV was carried out between +0.02 V and +0.9 V vs. SHE and the electrochemically active surface area was determined from the integrated area above the hydrogen adsorption portion of a voltammogram (corresponding to a voltage range of ca. +0.1 to +0.4 V), assuming a charge of 210 ⁇ /cm 2 to reduce one monolayer of hydrogen atoms on Pt.
  • MEAs were tested under the Fuel Cell Commercialization Conference of Japan's (FCCJ) standard start-stop potential cycling, and load cycling protocols. The goal of these accelerated degradation testing was to generate data for benchmarking and to gain a better understanding of the fundamental mechanisms related to cathode performance loss during fuel cell operation.
  • FCCJ Fuel Cell Commercialization Conference of Japan's
  • FIG. 8 schematically shows a start-stop cycling protocol according to one embodiment of the present invention.
  • this accelerated durability test simulates start-up and shut-down of a stack without the application of any operational controls that may mitigate fuel cell performance losses.
  • the anode and cathode are filled with ambient air and pinned to the air-air potential; introducing hydrogen gas causes a hydrogen-air front to move through the anode chamber, with a large shift in the cell potential ( as high as 1.5 V).
  • the start- stop durability protocol simulates this event many times by cycling from l.OV to about 1.5 V at a scan rate of 500 mV/s.
  • the carbon catalyst support in the cathode corrodes, degrading the operational performance of the fuel cell.
  • the protocol used in the present study essentially evaluates the corrosion of the cathode catalyst support and the corresponding loss in area of Pt. ECA measurements were conducted intermittently after a certain number of cycles up to 1000 cycles. In addition, the fuel cell performance of MEAs were evaluated at the beginning of life (BoL) and end of life (EoL) to understand the effect of carbon support corrosion on iV polarization curves.
  • Load cycling This accelerated durability potential cycling test simulates the high load and no load events that typically occur when a fuel cell vehicle is driven at different speeds. .
  • the MEA was cycled in steps between 0.60 V and 0.95 V to simulate peak load and OCV/idle.
  • the temperature, gas flow rate, and humidity operating conditions were the same as in the carbon corrosion test. Up to 10,000 voltage cycles were performed in a typical test. The voltage variations represent the largest oscillations that may be encountered during normal operation of a fuel cell vehicle stack.
  • carbon corrosion is insignificant and the major causes for power loss are Pt dissolution, agglomeration, and migration on the support and through the membrane.
  • Pt degradation was monitored by periodic measurement of the cathode Pt ECA and by comparing BoL and at the EoL i-V hydrogen/air fuel cell polarization curves.
  • FIG. 10 schematically shows polarization curves for 5 cm 2 MEAs with a Nafion 21 1 membrane and electrospun nanofiber electrodes with cathode and anode Pt loading of 0.10 ⁇ 0.005 mg/cm 2 according to one embodiment of the present invention, where ( ⁇ ) shows TKK TEC10E50E (Pt/HSAC), and ( ⁇ ) shows Johnson Matthey HiSpecTM 4000 (Pt/Vulcan).
  • Fuel cell operating conditions include: 80°C, 100% RH feed gases at ambient pressure, 125 seem H2 and 500 seem air.
  • the polarization curves for the two catalysts were essentially the same.
  • the TKK Pt/HSAC showed a modest advantage in current densities, but the difference was 10% at most, so there is no clear superiority of one catalyst material over the other.
  • FIG. 11 schematically shows fuel cell polarization curves for 5 cm 2 MEAs with TKK Pt/HSAC catalyst and NR21 1 membrane operated at 80°C with fully humidified 3 ⁇ 4/air at ambient pressure according to one embodiment of the present invention, where the weight ratios of Pt/HSAC : Nafion : PAA are: ( ⁇ ) 72: 13 : 15, ( ⁇ ) 63 :22: 15, and ( ⁇ ) 55:30: 15.
  • the cathodes and anodes used to obtain the polarization curves as shown in FIG. 1 1 are electrospun and have a Pt loading of 0.10 ⁇ 0.005 mg/cm 2 .
  • the fuel cell polarization curves only show marginal differences for the three different MEAs. Unlike a conventional non-structured electrode morphology, where binder content has a significant effect on the porosity and performance of the electrode [10], the nanofiber cathode power output was unaffected by changes in Nafion content.
  • FIG. 12 schematically shows fuel cell polarization curves for 5 cm 2 MEAs with TKK Pt/HSAC catalyst and NR21 1 membrane operated at 80°C with fully humidified H2/air at ambient pressure according to one embodiment of the present invention, where ( ⁇ ) shows electrospun fibers (with PAA), ( ⁇ ) shows painted GDE (no PAA), and ( ⁇ ) shows painted GDE (with PAA).
  • the cathodes and anodes used to obtain the polarization curves as shown in FIG. 12 have a Pt loading of 0.10 ⁇ 0.005 mg/cm 2 .
  • the MEA with PAA produced significantly less power than the PAA-free MEA.
  • Nanofiber Diameter Two methods were found to be most effective in controlling (decreasing) fiber diameter during electrospinning: (i) decreasing the wt.% Pt/C powder and total polymer (Nafion + PAA) in the ink from 18wt.% to 10 wt.% and (ii) the use of alcohol solvents of higher boiling points in the electrospinning ink. For a spinning solution with a Pt/C + Nafion + PAA content less than 10 wt. %, well-formed fibers could not be made (with ink electrosprayed into droplets). As shown in Table I, the diameter of electrospun nanofibers was effectively varied from 250 to 520 nm.
  • the solvent type and % alcohol in the ink are also listed in the table.
  • the Pt/C-Nafion- PAA composition was fixed at 63 wt.% Pt/C, 22 wt.% Nafion, andl5 wt.% PAA.
  • TKK Pt/HSAC catalyst powder was used in all of the inks.
  • the solvents used, in order of decreasing fiber diameter, were methanol, ethanol, isopropanol, and n-propanol.
  • FIG. 13 shows top-down 6,000x SEM images of an electrospun Pt/C/Nafion/PAA nanofiber mat with an average fiber diamter of (a) 250 nm and (b) 475 nm according to certain embodiments of the present invention, where the Pt/C catalyst used was TKK Pt/HSAC.
  • FIG. 13(a) is a mat with an average fiber diameter of 250 nm whereas the average fiber diameter of the mat as shown in FIG. 13(a) is 475 nm.
  • the mats were lightly pressed at room temperature onto conductive SEM tape and sputter coated with a thin layer of gold.
  • the general shape a generally uniform diameter along the length of a fiber
  • features i.e., roughened surface
  • Nanofiber MEAs were made from catalyst-coated membranes (CCMs) with nanofiber cathodes and anodes that were fabricated at Vanderbilt University. These electrodes had a fixed Pt/C:Nafion:PAA wt. ratio of 72: 13: 15 and an average fiber diameter of -400 nm. All MEAs were prepared with JM Pt/Vulcan catalyst cathodes and anodes, where the Pt loading of each electrode was 0.10 ⁇ 0.005 mg/cm 2 .
  • FIGS. 14A and 14B schematically show the effect of electrode structure on MEA performance with JM Pt/Vulcan catalyst using nanofiber electrode MEA and traditonal spray- coated MEA according to certain embodiments of the present invention, where FIG. 14A is at 100% RH, and FIG. 14B is at 40% RH. All data as shown in FIGS. 14A and 14B is recorded at 1 bar g pressure in air/3 ⁇ 4 at 80°C with NR211 membrane. As shown in the figures, the nanofiber MEA exhibited better performance than the spray-coated MEA under 100% RH condition (see FIG. 14A).
  • the improved performance of the nanofiber cathode is associated with an
  • FIGS. 15A and 15B schematically show the effect of electrode structure on MEA durability showing nanofiber electrospun and traditonal spray-coated MEAs using JM Pt/Vulcan catalyst according to certain embodiments of the present invention, where FIG. 15A is at 100% RH, and FIG. 15B is at 40% RH.
  • FIG. 15A for 100% RH operation the spray-coated MEA showed severe performance losses due to carbon corrosion, significantly more than the nanofiber electrode.
  • the EoL performance for the nanofiber electrode MEA was close to the BoL performance of the conventional spray-coated MEA, indicating excellent carbon corrosion resistance for the nanofiber morphology.
  • the sprayed electrode results are consistent with prior studies, where start-stop potential cycling resulted in , carbon support corrosion leading to electrode thinning, Pt loss (detachment of Pt particles), and significant electrode structure degradation, leading to drastic power output performance losses.
  • the carbon support also becomes more hydrophilic and retains more water, resulting in an increase in oxygen mass transport resistance.
  • FIG. 16 schematically shows real time measurement of ppm CO 2 at the cathode exhaust during start-stop potential cycling (100% RH condition) of nanofiber electrode and traditional spray-coated MEAs using JM Pt/Vulcan catalyst according to certain
  • FIG. 17 schematically shows carbon loss calculated from data as shown in FIG. 16 according to certain embodiments of the present invention.
  • FIG. 16 shows the amount of CO 2 detected as a function of time during carbon corrosion tests with the two different MEAs.
  • CO 2 generation increased with the number of potential cycles, illustrating the aggressive nature of this particular accelerated stress test.
  • repeated potential cycling has been found to be more aggressive than fixed potential hold durability tests [11].
  • the superior EoL performance of the nanofiber MEA at full humidity has been attributed to the combined effects of a higher ECA and the unique morphology of the nanofiber mats (inter and intra fiber porosity) that allows for the rapid expulsion of product water, thus preventing flooding. SEMs have confirmed that the nanofiber structure remains intact at EoL.
  • the performance losses for either MEA are not due to an increase in ohmic resistance, as the HFR remained unchanged for both spun and sprayed electrode MEAs at 100% RH.
  • the nanofibers also become more hydrophilic, but the structure still allows easier removal of water, allowing easier oxygen access to Pt sites.
  • the performance of the nanofiber MEA is even more impressive after voltage cycling when the power output was measured at 40% RH feed gas conditions.
  • the performance of the electrospun MEAs actually improved after the carbon corrosion test. Its EoL performance was significantly better than its BoL performance, even though there was a 20% carbon mass loss (as measured by CO 2 ).
  • carbon support oxidation was making the nanofibers more hydrophilic (better water retention properties) and less prone to drying during fuel cell operation at low RH and high feed gas flow rates.
  • the spray-coated MEA showed the same (expected) drop in EoL performance as was observed in the 100% RH polarization curve.
  • TKK TEC10E50E catalyst (Pt/HSAC) performed similarly as JM Pt/Vulcan in a nanofiber electrode MEA.
  • the performance of electrospun nanofiber MEAs with TKK was insensitive to changes in the fiber ionomer content (Nafion 13-30 wt. %).
  • Fuel cell performance with TKK TEC10E50E did not change significantly with average fiber diameter, in the range of 250-520 nm.
  • nanofiber MEA showed better performance than the spray- coated MEA under 100% RH condition. It is believed that the nanofiber structure provides more Pt catalyst active sites and these sites are more accessible to oxygen than in the case of traditional spray-coated electrodes, due presumably to a thinner binder (Nafion-PAA) layer covering the Pt catalyst particles. Under low RH conditions (40% RH), the electrospun electrodes showed significantly higher HFR and poor iV performance. The nanofiber structure may remove water faster than traditional spray-coated electrodes, resulting in sub- optimal catalyst layer hydration and/or drying effects under low RH test conditions.
  • nanofiber electrode MEAs showed both better initial power output and a less severe performance drop after start-stop durability cycling than traditional sprayed electrode MEAs.
  • nanofiber fuel cell electrodes were prepared with a polymer binder composed of Nafion and polyvinylidene fluoride, henceforth abbreviated as PVDF, or with just PVDF.
  • Nanofiber mat electrodes were incorporated into membrane electrode assemblies (MEAs) and tested in a hydrogen/air fuel cell. Experimental details follow. Preparing Inks and Electrosvinnins Fibers
  • Electrospinning inks with Nafion/PVDF binder were prepared by mixing in a
  • DMF/THF/acetone solvent (a) Johnson Matthey Company HiSpecTM 4000 (40% Pt on Vulcan carbon), (b) Nafion ® ion exchange resin, and (c) and Kynar HSV 900 polyvinylidene fluoride.
  • a suspension of Nafion and catalyst was first sonicated for 90 minutes with intermittent mechanical stirring before the addition of PVDF. The entire mixture was then mechanically stirred for approximately 15 hours. The total polymer and powder content of the spinning suspensions was between 10-18 wt%, and the Pt/C :Nafion: PVDF weight ratio was varied so the a dry mat contained 70 wt% Pt/C. 10-26 wt% Nafion and 4-20 wt% PVDF.
  • Electrospinning inks with PVDF binder were prepared by mixing in a DMF/acetone solvent: (a) Johnson Matthey Company HiSpecTM 4000 (40% Pt on Vulcan carbon) and (c) and Kynar HSV 900 polyvinylidene fluoride. A suspension of catalyst was first sonicated for 90 minutes with intermittent mechanical stirring before the addition of PVDF. The entire mixture was then mechanically stirred for approximately 15 hours. The total polymer and powder content of the spinning suspensions was 10 wt%, and the
  • Pt/C:PVDF weight ratio of a dry mat contained 70 wt% Pt/C. and 30 wt% PVDF.
  • the inks were drawn into a 3 mL syringe and electrospun using a 22-gauge stainless steel needle spinneret, where the needle tip was polarized to a potential of 12-16 kV relative to a grounded stainless steel rotating drum collector that was operated at a rotation speed of 100 rpm.
  • the spinneret-to-collector distance was fixed at 10 cm and the flow rate of ink was held constant for all experiments at 1.0 mL/h.
  • Nanofibers were collected on aluminum foil that was attached to the cylindrical collector drum. The drum also oscillated horizontally to improve the uniformity of deposited nanofibers. Electrospinning was performed at room temperature in a custom-built environmental chamber, where the relative humidity was maintained at 30-70%.
  • FIG. 18 schematically shows top-down 6,000x SEM image of an electrospun fiber mat with Pt/C catalyst particles with a binder of (a) Nafion+PVDF and (b) PVDF according to certain embodiments of the present invention.
  • the fiber composition is: 70 wt% catalyst, 20 wt% Nafion, 10 wt% PVDF.
  • the fiber composition is: 70 wt% catalyst, 30 wt% PVDF.
  • MEAs were created by hot pressing 5 cm 2 electrospun electrodes (anode and cathode) onto the opposing sides of a Nafion 21 1 membrane at 140°C and 4 MPa for 1 minute, after a 10-minute heating period at 140°C and 0 MPa.
  • the Pt loading of a nanofiber mat was calculated from its total electrode weight and the weight- fraction of Pt/C catalyst used in the electrospinning ink.
  • a 5 cm 2 carbon gas diffusion layer (Sigracet GDL 25 BCH) was physically pressed onto the MEA's anode and cathode when the MEA was placed in the fuel cell test fixture.
  • FIG. 19 schematically shows power density vs. current density curves for 5 cm 2 MEAs with a Nafion 21 1 membrane and cathode and anode Pt loading of 0.10 mg/cm 2 with Johnson Matthey HiSpec 4000 catalyst according to certain embodiments of the present invention.
  • the power densities of an MEA with an electrospun Nafion/PVDF binder cathode is shown in FIG. 19.
  • Fuel cell operating conditions are: 80°C, 100% RH feed gases at ambient pressure, 125 seem H2 and 500 seem air.
  • the new results are contrasted with an MEA with a electrospun Nafion/ poly(acrylic acid) (PAA) cathode and a traditional painted non-structured gas diffusion electrode with a Nafion binder.
  • PAA electrospun Nafion/ poly(acrylic acid)
  • FIG. 20 schematically shows power density and polarization curves for a 5 cm 2 MEA with a Nafion 21 1 membrane and a nanofiber cathode and anode according to certain embodiments of the present invention.
  • FIG. 20 the fuel cell performance of an MEA with an electrospun cathode with no Nafion (70 wt% catalyst and 30 wt% PVDF) is shown in FIG. 20.
  • This MEA had a maximum power of 291 mW/cm 2 .
  • the Pt loading for each electrode was 0.10 mg/cm 2 with Johnson Matthey HiSpec 4000 catalyst.
  • Cathode nanofiber mat had a compositoin of 70 wt/% Pt/C powder and 30 wt% PVDF.
  • the nanofiber anode had a composition of 65 wt% Pt/C powder, 23 wt% Nafion, and 12 wt% PAA.

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Abstract

Selon un aspect, la présente invention concerne un mat de fibres. Le mat de fibres comprend au moins un type de fibres, qui comprend un ou plusieurs polymères. Le mat de fibres peut être un mat de fibres unique qui comprend un type de fibres, ou peut être un mat de fibres double ou multiple qui comprend de multiples types de fibres. Les fibres peuvent en outre comprendre des particules d'un catalyseur. Le mat de fibres peut être utilisé pour former une électrode ou une membrane. Selon un autre aspect, un ensemble membrane-électrode de pile à combustible a une électrode d'anode, une électrode de cathode, et une membrane disposée entre l'électrode d'anode et l'électrode de cathode. L'électrode d'anode, l'électrode de cathode et la membrane peuvent chacune être constituées d'un mat de fibres.
PCT/US2014/057278 2010-10-27 2014-09-24 Solution de polymère, mat de fibres et ensemble membrane-électrode en nanofibres l'incluant, et son procédé de fabrication WO2016048309A1 (fr)

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CN201480082069.1A CN107408705A (zh) 2014-09-24 2014-09-24 聚合物溶液、纤维垫和具有所述纤维垫的纳米纤维膜电极组件以及其制造方法
KR1020177010681A KR20170062487A (ko) 2014-09-24 2014-09-24 중합체 용액, 섬유 매트, 및 그것을 갖는 나노섬유 멤브레인-전극-조립체, 및 그의 제조 방법
PCT/US2014/057278 WO2016048309A1 (fr) 2014-09-24 2014-09-24 Solution de polymère, mat de fibres et ensemble membrane-électrode en nanofibres l'incluant, et son procédé de fabrication
EP14902314.5A EP3198673A4 (fr) 2014-09-24 2014-09-24 Solution de polymère, mat de fibres et ensemble membrane-électrode en nanofibres l'incluant, et son procédé de fabrication
JP2017516107A JP2017535032A (ja) 2014-09-24 2014-09-24 ポリマー溶液、繊維マット、及びそれらを使用するナノ繊維膜−電極接合体、ならびに同接合体の製造方法
CA2962426A CA2962426A1 (fr) 2014-09-24 2014-09-24 Solution de polymere, mat de fibres et ensemble membrane-electrode en nanofibres l'incluant, et son procede de fabrication
US15/511,709 US20170250431A1 (en) 2010-10-27 2014-09-24 Polymer solution, fiber mat, and nanofiber membrane-electrode-assembly therewith, and method of fabricating same
US16/360,151 US20190245233A1 (en) 2010-10-27 2019-03-21 Inks for nanofiber fuel cell electrode and membrane-electrode-assemblies, and methods of ink formulations

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US13/823,968 Continuation-In-Part US9905870B2 (en) 2010-10-27 2011-10-27 Nanofiber electrode and method of forming same
US13/567,857 Continuation-In-Part US9350036B2 (en) 2010-10-27 2012-08-06 Composite membranes, methods of making same, and applications of same
US13/872,953 Continuation-In-Part US9252445B2 (en) 2010-10-27 2013-04-29 Nanofiber membrane-electrode-assembly and method of fabricating same

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US13/823,968 Continuation-In-Part US9905870B2 (en) 2010-10-27 2011-10-27 Nanofiber electrode and method of forming same
US15/511,709 A-371-Of-International US20170250431A1 (en) 2010-10-27 2014-09-24 Polymer solution, fiber mat, and nanofiber membrane-electrode-assembly therewith, and method of fabricating same

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WO2022169851A1 (fr) * 2021-02-02 2022-08-11 Plug Power Inc. Ensemble membrane-électrode d'électrolyseur d'eau à membrane échangeuse de protons

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JP7078902B2 (ja) * 2018-10-25 2022-06-01 株式会社豊田中央研究所 空気極触媒層
CN109841847A (zh) * 2019-03-11 2019-06-04 嘉兴学院 适用于金属空气电池的耐弯折柔性空气阴极的制备方法
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WO2022169851A1 (fr) * 2021-02-02 2022-08-11 Plug Power Inc. Ensemble membrane-électrode d'électrolyseur d'eau à membrane échangeuse de protons

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